1. Field of the Invention
The present invention relates a double clutch transmission which enables continuous gear ratio changes by a synchromesh mechanism which suppresses the disruption of power transmission to a minimum level using two clutches and two input shafts.
2. Description of Related Art
In automatic transmissions for vehicles (automobiles), there is a transmission referred to as a double clutch transmission which enables continuous gear ratio changes while suppressing the loss of power in transmission by utilizing a constant mesh (a constant mesh between drive gearwheels and driven gearwheels) gear mechanism.
In this double clutch transmission, a construction is adopted in which an input system which uses two input shafts having drive gearwheels and two clutches and an output system which uses two output shafts having driven gearwheels and synchromesh mechanisms are combined together. Specifically, as the input system, for example, a plurality of forward gears are divided into gear groups; a group of even-numbered gears and a group of odd-numbered gears, and drive gearwheels of the odd-numbered gear group are provided on either a first input shaft or a second input shaft which rotates on the periphery of the first input shaft, both the input shafts being connected to clutches, respectively, while drive gearwheels of the even-numbered gear group are provided on the other input shaft, whereby rotational power of an engine is transmitted to the first or second input shaft via the corresponding clutch. In addition, as the output system, a construction is adopted in which driven gearwheels, which are adapted to mesh with the mating drive gearwheels, are allocated together with synchromesh mechanisms on first and second output shafts which are provided in parallel to the first and second input shafts.
According to these input and output systems, for example, by making use of a duration when a gear shift of the odd-numbered gear group is completed and the rotational power of the engine inputted into the first input shaft from the corresponding clutch is changed in speed for output from one of the output shaft, a drive gearwheel for the next higher or lower gear on the even-numbered gear group is synchronized with a speed which is transmitted from the other output shaft by means of a synchromesh mechanism, so that a gear ratio change for the next higher or lower gear can be prepared. Because of this, when a currently active odd-numbered gear is shifted to the next higher or lower even-numbered gear, in the event that the clutch which is connecting the first input shaft to the engine is disengaged, while the other disengaged clutch is engaged to switch the power transmission to a transmission from the second input shaft, the currently active gear is shifted to the next higher or lower even-numbered gear on the spot. Furthermore, also when the currently active even-numbered gear is shifted to the next higher or lower odd-numbered gear, the next higher or lower odd-numbered gear on the first input shaft is synchronized with the vehicle speed for preparation for a gear shift to the next gear while the rotational power of the engine is transmitted via the second input shaft, a gear shift to the next higher or lower odd-numbered bear is completed. Therefore, gear shifts from low-speed gear to high speed gear, that is, a first gear to a sixth gear can be performed quickly and continuously while suppressing the loss of power or drive in transmission, that is, quick and continuous gear ratio changes can be performed from the first gear to the sixth gear.
In double clutch transmissions like this, as is disclosed in JP-A-2006-52832, it is normal practice to support rotatably an input shaft portion including a first and second input shaft by bearings.
Incidentally, since bearings at both ends of the input shaft portion each have to bear large load, a quite good lubrication is required to lubricate the respective bearings.
In a related art, in a transmission, lubricating oil which is collected in an oil reservoir located below an output shaft is splashed by driven gearwheels provided on the output shaft so as to produce a lubricating oil atmosphere in an interior of the transmission for lubrication of the bearings.
In the double clutch transmission, however, there exists a tendency that sufficient lubrication cannot be attained only by the lubricating oil atmosphere.
As a countermeasure against this tendency, as is disclosed in JP-A-2006-52832, it is a related practice to provide a separate lubricating oil supply mechanism with a view to securing a required lubricating performance.
Consequently, adding the same mechanism has led to problems that the size of the resulting double clutch transmission is enlarged, the construction thereof becomes complex, and costs that are borne by manufacturers are increased, and therefore, there have been demands for different methods.